As is well known, anisotropic magnetoresistance (AMR) causes a change in resistance of a thin strip of ferrous material when a magnetic field is applied perpendicular to a current flowing in the strip. Magnetic field sensors based on AMR characteristic of ferrous materials are also well known, as is the fact that these types of magnetometers need to apply an external magnetic field in order to set or reset the magnetic domain structure of the device after a large magnetic field disruption. The set/reset (S/R) field is usually generated by conductive coils either underneath or above the plane of the magnetic field sensing layer of the device. Based on Ampere's law, the field generated by the conductive coils is proportional to the current applied, thus, current strength is directly proportional to set or reset efficiency. Higher currents, however, come with a power consumption penalty that may outweigh any increase in sensor reliability or accuracy.
The modern electronic compass requires the magnetometer to be effectively used in a relatively high magnetic field environment, such as those found in smart phones or tablet computers. Increasing the effectiveness, however, usually requires a stronger set/reset field, which would be generated by a higher current and, therefore, would increase power consumption.
What is needed, therefore, is an accurate magnetic field sensor that is small in size, of low cost, that requires low power as is necessitated by mobile device applications, is easy to use and that is easily incorporated into a mobile device.